Diagnostic imaging systems are conventionally used in numerous medical procedures. These systems often require scan conversion techniques. For example, intravascular ultrasound systems scan within an area of interest in a vessel using a rapidly rotating catheter-mounted transducer transmitting ultrasound pulses and receiving returned echo signals. The detected ultrasound echo signals correspond to a particular R, .theta. location in the area of interest. For example, at a particular .theta., echo signals are received corresponding to a radial distance R1, R2, etc., forming what is conventionally known as a vector of data signals. Other vectors at varying values of .theta. are collected to complete a scan of the area of interest. Although the data is collected according to R, .theta. locations, CRT displays using conventional raster scans display pixels according to Cartesian or X, Y locations. Each screen pixel display element has an X, Y coordinate position within a raster scan. This X, Y coordinate position must be mapped back to a correlated location in the area of interest in order to assign a screen pixel display level, thus forming an image on the display. The correlated location in the area of interest will not ordinarily correspond to the R, .theta. location of collected data. Accordingly, the screen pixel display level is generated by interpolating the signals corresponding to echoes from R, .theta. locations adjacent to the correlated location. The mapping and interpolation of data from R, .theta. to X, Y coordinates prior to CRT display is known as scan conversion.
Scan conversion and display of diagnostic images is complicated by the desires of clinicians who, in real time, want to: a) image as much of the area of interest as possible, but also b) display as much detail as possible in the resulting image. Numerous conventional "Zoom" techniques may be used to magnify portions of a main or orientation image while still displaying the full depth of the area of interest in the main image. However, prior art solutions implementing "zoom" techniques did not perform simultaneous and independent scan conversion of the main image and the magnified image.
For example, Roundhill et al., U.S. Pat. No. 5,471,989, disclose a system for processing zoom ultrasonic images. The user outlines a portion of a displayed image. The outlined portion of the image is then enlarged to occupy the larger area of the original image. Although Roundhill et al. disclose a varying filter bandwidth optimized to maximize information content of the displayed image, their system does not independently scan convert the main and magnified image windows for simultaneous display. Thus, there is a need in the art for an imaging system which can independently process a main and a magnified image simultaneously. The present invention provides a system which allows the display of both small and high magnification at the same time but in different regions of the image.